Polyolefins are of great interest in industry as they have many uses in different areas. Polyolefins, such as polyethylene and polypropylene, are used in everything from waxes and plasticizers to films and structural components. Of late, many have been interested in modifying the architecture of such polyolefins in the hopes of obtaining new and better properties.
Vinyl terminated polymers, including homopolymers of polypropylene and copolymers of ethylene and polypropylene, are known to be useful for post-polymerization reactions due to the available ethylenic unsaturation in one polymer, at one chain end or both. Such reactions include addition reactions, such as those used in grafting other ethylenically unsaturated moieties, and further insertion polymerization where the vinyl terminated polymers are copolymerized with other monomers such as α-olefins and/or other insertion polymerizable monomers.
Vinyl chain ends are generally accepted to be more reactive to chain-end functionalization and insertion in subsequent polymerization reactions than are the other types. Such polymers with a high percentage of vinyl terminal bonds would be desirable for use in the preparation of branched polymers. Accordingly, a need exists for catalysts capable of forming polymers with a high percentage of vinyl terminal bonds.
Alt, Helmut G., et al., Journal of Organometallic Chemistry, vol. 514, issues 1-2, pp. 257-270 (1996), uses certain 3-, 4-, 3-, 4-, and 4,5-substituted zirconocene complexes of the type (C13H8-nRnCR′2C5H4)ZrCl2, where n is 1 or 2, R is an alkyl or aryl, and R′ is Me or Ph for polypropylene polymerizations. At a polymerization temperature of 62° C., the article reports an activity of 9.3 kg/mmol of catalyst per hour, an Mn of 29,000, and a Tm of 107.9° C. There is no indication, however, that these catalysts produce polymers with vinyl chain ends.
Siedle, A. R., et al., Journal of Molecular Catalysis A: Chemical, vol. 191, issue 2, pp. 167-175 (2003) discusses an asymmetry parameter applied to ansa-bridged metallocene catalysts of the type [(ligand 1)-bridge-(ligand 2)MX2 where ligands 1 and 2 are variously substituted cyclopentadienyl, indenyl, or fluorenyl groups connected by, e.g., SiMe2 or C2H4 and where M is Ti, Zr, or Hf, and X is a halogen or alkyl group. The asymmetry parameter is defined as the ratio of the van der Waals area of ligand fragment 1 to that of ligand fragment 2. A series of syndioregulating catalysts were used to polymerize propylene. As the catalyst asymmetry parameter increases, the polypropylenes produced are said to have successively higher syndiotacticity. WO 99/20664 claims a metallocene catalyst of the type [(ligand 1)-bridge-(ligand 2)MX2, where ligand 1 and ligand 2 are different and may include substituted and unsubstituted cyclopentadienyl, indenyl, and fluorenyl groups, the catalyst having an asymmetry parameter of 1.03 to 1.69. WO 99/20664 discloses a catalyst, {flu-CMe2-Cp}ZrCl2, having an asymmetry parameter of 2.09.
Other references of interest include: WO 2012/134715 and US 2005/148460.
The presence of long chain branching may lead to improved processability and some improved end-use properties in certain polymers. For instance, long chain branching may result in polymers exhibiting improved melt elasticity and/or improved shear thinning. Polymers produced using conventional Ziegler-Natta catalysts may have long chain branching, but such conventional processes are often more expensive than newer technologies using metallocene catalysts. Metallocene based polymers, however, typically lack long chain branching.
There is still a need for new and improved metallocene catalyst systems for the polymerization of olefins, in order to achieve specific polymer properties, such as polymers with a high percentage of vinyl terminal bonds and higher molecular weights, and polymers with long chain branching. The present invention provides novel catalyst compounds capable of meeting these needs, catalysts systems comprising such compounds, and processes for the polymerization of olefins using such compounds and systems.